A pacemaker the size of a pill has been fitted inside the heart of a UK patient in a revolutionary new operation.

The wireless device used for the first time in the country at Southampton General Hospital, known as the Micra Transcatheter Pacing System, is the smallest in the world at one-10th the size of traditional models and is implanted directly in the heart.

Currently, pacemakers are inserted under the skin via an incision in the chest and connected to the heart via a lead which carries electrical signals to correct slow or irregular heartbeats - but they can require replacement due to broken or dislodged wires.

The new device, which is placed inside the wall of the heart by a catheter passed up through the groin, delivers electrical impulses from an electrode, removing the need for a lead to transmit signals.

Professor John Morgan, consultant cardiologist, said: "While pacemakers have saved countless thousands of lives over the past seven decades since the first devices were implanted, one of the major drawbacks has been complications related to the pacing lead that is put in to deliver electrical impulses to the heart.

"Now we have pacemakers that are so small - not much larger than an antibiotic pill - they can be attached directly to the inside of the heart, all the problems related to the old-fashioned pacemaker lead are abolished."

Prof Morgan, who is also honorary chair in cardiac rhythm management at the University of Southampton, said the introduction of the device and launch of the study was a "landmark moment".

He added: "In addition to the advantages of the device's size and wireless technology, the procedure reduces the risk of infection and extended recovery time associated with traditional, more invasive surgical pacemaker implants.

"This a big step forward in patient treatment and a milestone for cardiac rhythm management in the UK."